Title: Linear and non-linear THz spectroscopy of collective excitations in correlated materials
Host: Cyrus Dreyer
In this talk, I will discuss two new aspects of time-domain THz spectroscopy on strongly correlated materials. In the first case, we combine THz spectroscopy and inelastic neutron scattering measurements on the quantum spin liquid candidate YbMgGaO4 to obtain better insight into its exchange interactions. THz spectroscopy in this fashion functions as high-field electron spin resonance and probes the spin-wave excitations at the Brillouin zone center, ideally complementing neutron scattering. This study strongly constrains possible mechanisms responsible for the observed spin-liquid phenomenology. In the second case, I will discuss how we apply the new technique of non-linear THz two-dimensional coherent spectroscopy to extract the first measurements of energy relaxation ( decoherence ( T2 ) times close to the insulating side of the 3D metal-insulator transition (MIT) in phosphorus doped silicon. I will argue how the observed features imply that a strongly disordered interacting insulator cannot be mapped to a system of effectively non-interacting localized excitations. We dub this new phenomenology a “marginal Fermi glass”.
Xinshu Zhang, Fahad Mahmood, et. al. Physical Review X 8, 031001 (2018)
Fahad Mahmood, et. al. arXiv:2005.10822 (2020)